sctp: make sure stream nums can match optlen in sctp_setsockopt_reset_streams

Now in sctp_setsockopt_reset_streams, it only does the check
optlen < sizeof(*params) for optlen. But it's not enough, as
params->srs_number_streams should also match optlen.

If the streams in params->srs_stream_list are less than stream
nums in params->srs_number_streams, later when dereferencing
the stream list, it could cause a slab-out-of-bounds crash, as
reported by syzbot.

This patch is to fix it by also checking the stream numbers in
sctp_setsockopt_reset_streams to make sure at least it's not
greater than the streams in the list.

Fixes: 7f9d68ac ("sctp: implement sender-side procedures for SSN Reset Request Parameter")
Reported-by: NDmitry Vyukov <dvyukov@google.com>
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Acked-by: NMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/socket.c

@@ -3891,13 +3891,17 @@ static int sctp_setsockopt_reset_streams(struct sock *sk,
 	struct sctp_association *asoc;
 	int retval = -EINVAL;
 
-	if (optlen < sizeof(struct sctp_reset_streams))
+	if (optlen < sizeof(*params))
 		return -EINVAL;
 
 	params = memdup_user(optval, optlen);
 	if (IS_ERR(params))
 		return PTR_ERR(params);
 
+	if (params->srs_number_streams * sizeof(__u16) >
+	    optlen - sizeof(*params))
+		goto out;
+
 	asoc = sctp_id2assoc(sk, params->srs_assoc_id);
 	if (!asoc)
 		goto out;